Quality of life improvements in Squiggle editor

[NunoSempere]

• Show the mean, standard deviation, and the different CI again
• Allow people to specify the x axis. This is useful for displaying the first part of a distribution with really long tails
• Have better toggles, rather than the current log y scale / log x scale, which look pretty ugly

[Hazelfire]

Was talking to Ozzie about 1 and 2 here. So hopefully we'll see this soon!